• Welcome to The Truck Stop! We see you haven't REGISTERED yet.

    Your truck knowledge is missing!
    • Registration is FREE , all we need is your birthday and email. (We don't share ANY data with ANYONE)
    • We have tons of knowledge here for your diesel truck!
    • Post your own topics and reply to existing threads to help others out!
    • NO ADS! The site is fully functional and ad free!
    CLICK HERE TO REGISTER!

    Problems registering? Click here to contact us!

    Already registered, but need a PASSWORD RESET? CLICK HERE TO RESET YOUR PASSWORD!

mahle 18:1 pistons discontinued- how much will 10 thou drop my comp ratio?

J.Peart

J.Peart

Active Member
Messages
160
Reaction score
51
Location
Kelowna, bc, canada
Basically what the title says. spent weeks trying to get the Mahle 18:1 marine pistons (027060HAWR-040) ordered. finally got things sorted out and then they find out from Mahle they have been discontinued.

So i have opted to go standard pistons topped 10 thou (02701HAWR-040) for use with a decked block. my block is not decked, so how much will the extra 10 thou drop my comp ratio?

thanks,
James
 
That sucks, guess I'll have to stick a Dmax in the 93. Why did they quit making them, where does Peninsular/GEP get there 18:1 slugs?

I'm running the .010 thicker felpro head gasket now, this would accomplish the same thing if you dont need new pistons.
 
I remember that if you cut the crown of the piston, you are asking for issues. If you do that, you will be removing the anodized coating that protects the aluminum from the extreme heat.

I would call Peninsular Diesel. They sell low compression pistons.
 
John Kennedy had them on sale a while ago, not sure if they still are...
 
Last edited by a moderator:
Yeah i know about kennedy's pistons, but they are stock pistons which get machined as far as i know. I wanted pistons that were manufactured like that rather than machined down. which is when i went for the 10 thou decked mahles.

I wonder where pennisular gets theirs- maybe ill call them up.
 
Dang, it's a sad day, no more Mahle 18:1's, -what a suck that is.

Hey Chicago, -weren't those 18:1's you used to have a few years back Zollners?

Is Zollner still making pistons? -Or have they gone by the wayside too?



Well, -not that it would be a first choice, but you could always run the -.010" Mahle's along with +.010" felpro gaskets, -that'd get ya around 19:1, -which would be just about right.
 
Why not just get the pistons re-hard anodized? It's not that big of a deal.... If you really want a better protection to the pistons then get them coated.
 
Or........Leave the piston's alone and resize the rods and make them .020 or .030 shorter. This will drop you compression and you will only need to check your piston skirt clearence which will not hurt you in any way if you had to take away material from the skirt.
 
how safe is that? to resize the con. rods? wouldn't that be cheaper all around if it worked the same? I am wondering about location of the oil ring when the piston is dropped lower in the cylinder with the same ring spacing
 
.030 is very small. Think of this, .002 is the average thickness of a human hair. If .010 shaved off and a .010 thicker head gasket is good for 19:1 then you can shorten the rods .020 and be done with it. the oil rings at even .100 wouldn't come close from coming through the bottom of the cylinder. If it is too short then piston skirt to crank would be the issue. But we are taking about .030. On stroker motors this is a normal practice but when you stroke a SBC to a 383 you are adding .250 more stroke than stock. A quarter of an inch! Not .030 but .250. Simple machine work.
 
so how much would have to be take off to equal an appox 18:1?

Jpeart: where in Kelowna are you? I have probably seen your truck around town.
 
To do it right you would need to cc your combustion chamber of the heads and try to match them all. Measure the block and square it. Deck it if needed. Throw in the piston and measure the deck. With these figures you can determine the current compression ratio. Then adding the volume of the piston deck area + the added drop in the cylinder you will be able to determine what it needs to be to have 18:1. Every motor and every head are a little different from each other so dimensions will vary.
 
Remember deck height plays a part in compression ratio also.

Don't have all the specs for my motor but with the block that was used for my motor .005 shorter rods and .010 shorter pistons made a 20:1 motor.
 
GJF said:
.030 is very small. Think of this, .002 is the average thickness of a human hair. If .010 shaved off and a .010 thicker head gasket is good for 19:1 then you can shorten the rods .020 and be done with it. the oil rings at even .100 wouldn't come close from coming through the bottom of the cylinder. If it is too short then piston skirt to crank would be the issue. But we are taking about .030. On stroker motors this is a normal practice but when you stroke a SBC to a 383 you are adding .250 more stroke than stock. A quarter of an inch! Not .030 but .250. Simple machine work.
Click to expand...


And not all 383s have to have the skirts modified. Depends on what combination of parts you use.
 
GJF is on his game, I agree with everything he has stated 100%.

Also keep in mind, offset grinding the crank is also an option, -that COULD yield another .010" -if needed.

Again, not a first choice, -but still a viable option.

In my opinion, -a 19:1 motor will still open a huge door for safe elevated boost levels.

There IS a shop I use in Seattle that is fully capable of doing ceramic coating (titanium dioxide). I was under the impression that the piston tops were ceramic, not anodized, -am I wrong?

The Mahle's and Zollners I've seen sure look like ceramic, -with carbon graphite skirts.

Sure is a shame we can't get these anymore.
 
I believe that OE was anodized in the later engines. The first turbo engines were plain aluminum with no coating and I believe 93-94 started anodizing them. I think that KENNEDY was using a ceramic coating on his after they were machined to spec for the reduced compression ratio. His pistons were using an enlarged bowl area in the piston to concentrate the combustion directly over the piston to reduce power loss to the cylinder walls.
 
You must log in or register to reply here.
Back
Top